i like boo. it kind of is c# with a python-like syntax. so your code will be much shorter.

boo is easy to figure out if you know some python and some c# or java. there aren't many tutorials and examples though for unity so probably for most people it's best to learn c#. boo also can't be used for unity-iphone at the moment but there are pretty good c#<->boo converters i think.

by the way, unity doesn't use javascript. it's unityscript which only looks like javascript at a first glance but there are many differences. i wouldn't use it since it's proprietary and you can only use it with unity. as far as i know unityscript actually is boo in disguise. they used boo for creating it since boo has powerful language and compiler extension features.